There are a lot of great solutions to your problem, but to upgrade your trailer axles from 6,000 lbs to 7,000 lbs, you need to replace your axles entirely. Adding higher capacity hubs alone won't change the weight capacity of your axles. Note that even if you decide to upgrade your axles, you still might be limited by the weight capacity of your trailer frame or coupler as these could be rated less than your axle capacity.
To upgrade your axles, I recommend a full kit that includes a 7,000... view full answer...